[PATCH] D103304: Update and improve compiler-rt tests for -mllvm -asan_use_after_return=(never|[runtime]|always).

[Evgenii Stepanov via Phabricator via llvm-commits]

eugenis added a comment.

`__asan_detect_use_after_return`, any variant of it, is not entirely correct. First, using the presence of the global is better than its value, because the linker will pick a random instance in case they disagree, while `&(...) != nullptr` gives reliable OR semantics.

Second, this does not handle `dlopen` out of the box. It can be almost fixed by calling something from a library constructor (like __asan_init) and passing the address/value of the UAR setting, but even that is not 100% correct as code from a library may run before any of that library's constructors. It will also require late-initialization of fake stack on all existing threads at the time of `dlopen`.

Lazy init would work, but need to make sure that fake stack init is async signal safe, because the first use in a thread may be in a signal context. Another option is to make sure that unused fake stack is cheap, and initialize it always. I don't know if that is the case right now.

Having said all this, the implementation in this revision will kind of work in most cases, and the worst consequence of a mistake is some performance loss, so I'm fine with the change as is.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D103304/new/

https://reviews.llvm.org/D103304